The present invention relates to an optical disk on which information has been recorded with high density and an optical disk apparatus for reproducing the information recorded on the optical disk.
To meet demands that MPEG2 compressed image information should be recorded on one side of a 12-cm-diameter optical disk for more than two hours, DVD systems have been commercialized. In the DVD standard, a disk has a storage capacity of 4.7 GB on one side, a track pitch (the width of each track) of 0.74 xcexcm/track, and a bit pitch (the length of one data bit on a track) of 0.267 xcexcm/bit. Hereinafter, DVD complying with the standard is called the current DVD.
The information recorded on an optical disk such as DVD is reproduced using an optical head. In the optical head, an objective lens gathers beams of light emitted from an LD (laser diode) onto a pit pattern on a track on the optical disk. The light beam reflected by the optical disk is gathered by a condenser lens onto a photo detector, which produces a reproduced signal. The reproduced signal from the photo detector is inputted to a reproduced signal processing system. After the signal is waveform-equalized at an equalizer, it is decoded into the data at a signal detector. In the DVD standard, the wavelength of LD in the optical head is 0.65 xcexcm and the numerical aperture NA of the objective lens is 0.6.
In the current DVD system, a waveform slicing scheme is generally used as a reproduced signal processing scheme. The waveform slicing scheme will be explained by reference to FIG. 1.
On an optical disk, a pit pattern C is formed according to the recording waveform B corresponding to recording data A, the information to be recorded.
When the information thus recorded on the optical disk is reproduced, the LD in the optical head projects a light beam for reproduction on the optical disk in the form of a very small beam spot as shown by the shaded portion in the figure, reads the pit pattern, and produces a reproduced signal. The waveform of the reproduced signal (reproduced waveform) is not a rectangular waveform like recording waveform B, but dull reproduced waveform D because of the characteristics of the recording and reproducing system.
Then, the equalizer subjects the reproduced waveform to waveform equalization in such a manner that the intersection of equalized waveform E and a certain set threshold value (shown by a single-dot-dash line) becomes the center of the window. Specifically, the high-frequency components of the reproduced signal are amplified. The signal detector detects the intersection of equalized waveform E and the threshold value and outputs binary data F as follows: if it has detected the intersection within the window, it will output xe2x80x9c1,xe2x80x9d and if not, it will output xe2x80x9c0.xe2x80x9d Then, the binary data F obtained in the intersection detection is subjected to NRZI (Non-Return-to-Zero Inverted) conversion, thereby producing decoded data G.
Optical disks have been required to have much higher density. For example, effort has been directed toward developing a high-definition DVD system capable of recording high-definition images on one side of a 12-cm-diameter disk for more than two hours. The storage capacity required of high-definition DVD is 15 GB/side. Therefore, the high-definition DVD is required to have 3.19 (≈15/4.7) times as high a density as that of the current DVD.
However high the density is made, the signal degrading components increase, as long as the waveform slicing scheme as described above is used as a method of processing the reproduced signal in the system. This makes it impossible to decode the data correctly. Therefore, it is desirable that, instead of the waveform slicing scheme, a PRML (Partial Response and Maximum Likelihood) scheme should be used as a reproduced signal processing scheme to avoid a decrease in SNR.
To make an optical disk have a high density by the PRML scheme, not only is the performance brought out fully, but also conditions under which the information recorded on the optical disk is reproduced correctly have to be found. From these viewpoints, examination must be made as to in what ratio an increase in the recording density to be achieved by the PRML scheme should be allocated to the track pitch and bit pitch. Such an examination has not been made.
Accordingly, it is an object of the present invention to provide an optical disk which, even if the density is made higher than a reduction in the beam spot, enables information to be reproduced correctly, as compared with the current DVD, by allocating an increase in the recording density achieved by the PRML scheme as a reproduced signal processing scheme, to the track pitch and bit pitch suitably, and an optical disk apparatus for reproducing the information from the optical disk.
According to one aspect of the present invention, there is provided an optical disk on which information is recorded at a track pitch of TP xcexcm/track and a bit pitch of BP xcexcm/bit on the basis of a modulation code with a minimum run of D and a code rate of R and from which the information is reproduced using a light source emitting a light beam whose wavelength is xcex xcexcm and an objective lens whose numerical aperture is NA, the optical disk fulfilling the following conditions:
TP greater than xcex/(2NA),
BP greater than {1/(2(D+1)R)}xc2x7{xcex/(2NA)},
TPxc2x7BPxe2x89xa6(0.168/n)xc2x7(xcex/NA)2, and
0.361xe2x89xa6BP/TP less than 1/{(D+1)R},
where n is a real number greater than 1.
According to another aspect of the present invention, there is provided an optical disk on which information is recorded at a track pitch of TP xcexcm/track and a bit pitch of BP xcexcm/bit on the basis of a modulation code with a minimum run of D and a code rate of R and from which the information is reproduced using a light source emitting a light beam whose wavelength is xcex xcexcm and an objective lens whose numerical aperture is NA, the optical disk fulfilling the following conditions:
TP greater than xcex/(2NA),
BP greater than {1/(2(D+1)R)}xc2x7{xcex/(2NA)},
TPxc2x7BPxe2x89xa6(0.168/nxc2x7(xcex/NA)2, and
0.361xe2x89xa6BP/TP less than 0.361n,
where n is a real number greater than 1.
According to still another aspect of the present invention, there is provided an optical disk on which information is recorded at a track pitch of TP xcexcm/track and a bit pitch of BP xcexcm/bit on the basis of a modulation code with a minimum run of D and a code rate of R and from which the information is reproduced using a light source emitting a light beam whose wavelength is xcex xcexcm and an objective lens whose numerical aperture is NA, the optical disk fulfilling the following conditions:
TP greater than xcex/(2NA),
BP greater than {1/(2(D+1)R)}xc2x7{xcex/(2NA)},
TPxc2x7BPxe2x89xa60.135(xcex/NA)2, and
0.361xe2x89xa6BP/TP less than 1/{(D+1)R}.
According to still another aspect of the present invention, there is provided an optical disk on which information is recorded at a track pitch of TP xcexcm/track and a bit pitch of BP xcexcm/bit on the basis of a modulation code with a minimum run of D and a code rate of R and from which the information is reproduced using a light source emitting a light beam whose wavelength is xcex xcexcm and an objective lens whose numerical aperture is NA, the optical disk fulfilling the following conditions:
TP greater than xcex/(2NA),
BP greater than {1/(2(D+1)R)}xc2x7{xcex/(2NA)},
TPxc2x7BPxe2x89xa60.135(xcex/NA)2, and
0.361xe2x89xa6BP/TP less than 0.451.
According to still another aspect of the present invention, there is provided an optical disk apparatus comprising: an optical disk on which information is recorded at a track pitch of TP xcexcm/track and a bit pitch of BP xcexcm/bit on the basis of a modulation code with a minimum run of D and a code rate of R; a light source for emitting a light beam whose wavelength is xcex xcexcm; an objective lens whose numerical aperture is NA, the objective lens sending the emitted light beam to the optical disk; and a processing unit for processing the information from the optical disk by a PRML (Partial Response and Maximum Likelihood) scheme, wherein the optical disk fulfills the following conditions:
TP greater than xcex/(2NA),
BP greater than {1/(2(D+1)R)}xc2x7{xcex/(2NA)},
TPxc2x7BPxe2x89xa60.168/n)xc2x7(xcex/NA)2, and
0.361xe2x89xa6BP/TP less than 1/{(D+1)R},
where n is a real number greater than 1.
According to still another aspect of the present invention, there is provided an optical disk apparatus comprising: an optical disk on which information is recorded at a track pitch of TP xcexcm/track and a bit pitch of BP xcexcm/bit on the basis of a modulation code with a minimum run of D and a code rate of R; a light source for emitting a light beam whose wavelength is xcex xcexcm; an objective lens whose numerical aperture is NA, the objective lens sending the emitted light beam to the optical disk; and a processing unit for processing the information from the optical disk by a PRML (Partial Response and Maximum Likelihood) scheme, wherein the optical disk fulfills the following conditions:
TP greater than xcex/(2NA),
BP greater than {1/(2(D+1)R)}xc2x7{xcex/(2NA)},
TPxc2x7BPxe2x89xa60.168/n)xc2x7(xcex/NA)2, and
0.361xe2x89xa6BP/TP less than 0.361n,
where n is a real number greater than 1.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.